Delhi overtakes Lahore as world's most polluted city as air quality drops

India's capital, Delhi, overtook Lahore in Pakistan to become the world's ​most polluted city on Friday, with ‌air quality reaching hazardous levels and visibility dropping as smog blanketed the city of 20 million ​people.

Air quality index (AQI) in Delhi was "hazardous" ​at 334, making it the most ⁠polluted major city globally, according to Swiss ​group IQAir, which measures air quality levels ​based on the concentration of toxins.

An AQI reading up to 50 is considered good with little or ​no health risk. India's official Central Pollution ​Control Board pegged the AQI higher at 403 and ‌rated ⁠it "severe".

The Swiss and Indian readings vary due to the different AQI scales and methodologies used to calculate and classify air pollution ​levels.

Cars and ​motorcycles emerged from ⁠dense smog, which also appeared to obscure street lights on the ​city's main roads, videos from ​news ⁠agency ANI showed.

Pollution is a seasonal problem in many parts of northern India and neighbouring Pakistan, ⁠as the ​cold, heavy air of ​winter traps vehicle emissions, construction dust and smoke from agricultural ​burning.

Read: Lahore tops global pollution rankings as AQI crosses 500 in several Punjab cities

A day earlier, Lahore remained the world’s most polluted city on the global air quality rankings, while several cities across Punjab recorded Air Quality Index (AQI) levels of 500 or higher, as air pollution continued to pose a serious health risk.

A recent report by the Pakistan Air Quality Initiative (PAQI) also found that air pollution in Lahore increased by 32 per cent compared to the corresponding period last year.

According to Punjab’s air quality monitoring data, Lahore today recorded an AQI of 346 at 8am, compared to 444 at the same time a day earlier, marking a decline of 98 points in 24 hours.

However, pollution levels remained extremely high. IQAir recorded Lahore’s AQI at different times at 344, 363 and 371, with the city retaining the top position in its global pollution rankings. New Delhi ranked second.

Air quality conditions were also alarming in other parts of Punjab. According to IQAir, Raiwind recorded an AQI of 519, Bahawalpur 515 and Multan 507, while Gujranwala registered 411.

Punjab’s air quality monitoring network also recorded AQI levels of up to 500 in Kasur, Jhang, Nankana Sahib, Okara, Pakpattan and Sahiwal.